Porosity Effects on Cyclic Gas Invasion and Trapping in Deformable Porous Media
Pith reviewed 2026-06-29 02:06 UTC · model grok-4.3
The pith
Gas trapping in deformable porous media rises with decreasing porosity and repeated injection cycles due to evolving interactions.
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
Core claim
Gas trapping depends on both the initial packing structure and the cyclically evolving gas-solid interactions. Experiments in a Hele-Shaw cell with hydrogel particles show that lower porosity increases gas entry pressure according to pore-throat estimates, shifts invasion from cavity expansion to pore invasion, produces more frequent small pressure fluctuations, and results in higher residual gas saturation that grows with each cycle. Interfacial length scales with gas cluster size via a power law whose exponent decreases at lower porosity and with more cycles.
What carries the argument
Porosity-dependent invasion regimes and cyclic pressure evolution during repeated gas-water injections in packs of soft hydrogel particles
If this is right
- Gas entry pressure increases as porosity decreases, consistent with Young-Laplace based on effective pore-throat width.
- Invasion shifts from cavity-dominated expansion in high-porosity packings to localised pore invasion in low-porosity ones, with a mixed regime at intermediate porosity.
- Low-porosity packings produce frequent small-amplitude pressure drops while higher-porosity ones show more discrete relaxations.
- Residual gas saturation increases systematically with injection cycles and reaches higher terminal values as porosity decreases.
- Specific interfacial length follows a power-law with gas cluster size, with the scaling exponent decreasing as porosity decreases and cycling progresses.
Where Pith is reading between the lines
- The power-law interface scaling might allow prediction of long-term trapping amounts from early-cycle observations in similar systems.
- Preferential pathway reuse over cycles could mean that after a few injections, further gas addition stabilizes rather than increases trapped amounts.
- Applications involving repeated fluid cycles, such as gas storage or biological fluid transport, may need to track both initial density and interaction history to forecast final trapped fractions.
Load-bearing premise
The quasi-2D Hele-Shaw geometry and hydrogel particle mechanics produce invasion and trapping statistics representative of three-dimensional natural deformable porous media.
What would settle it
Performing the same cyclic injection experiments in a three-dimensional packing of soft particles and finding substantially different porosity dependence in residual saturation or invasion patterns would falsify the representativeness claim.
read the original abstract
Fluid transport in deformable porous media is central to many biophysical and geophysical processes. While extensive studies exist, how porosity governs fluid behaviour in deformable systems during cyclic injection remains elusive. Here, we investigate gas-liquid multiphase flow in a quasi-2D Hele-Shaw cell packed with soft hydrogel particles at different initial porosities. Alternative gas and water injection experiments, combined with high-resolution imaging and continuous pressure monitoring, are used to quantify gas dynamics and pressure evolution. Results show that the gas entry pressure increases as porosity decreases, consistent with a Young-Laplace estimation based on effective pore-throat width. After entry, invasion shifts from cavity-dominated expansion in high porosity packings to localised pore invasion in low porosity packings, with a mixed cavity-fingering regime at intermediate porosity. Pressure fluctuations are linked to pore-scale gas escape and internal gas redistribution. Low porosity packings produce frequent small-amplitude pressure drops, whereas higher porosity packings produce more discrete pressure relaxations. Across cycles, the decreasing mean pressure suggests preferential-pathway reuse and reduced local capillary constraints. Residual gas saturation increases systematically with injection cycles and reaches higher terminal values as porosity decreases. Specific interfacial length increases as available pore space decreases and follows a power-law relationship with gas cluster size, with scaling exponent decreases as porosity decreases and cycling progresses. Together, these results demonstrate that gas trapping in deformable porous media depends on both initial packing structure and cyclically evolving gas-solid interactions. This study provides insights for interpreting porosity-dependent trapping and reinvasion during repeated gas injection.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The manuscript reports an experimental investigation of cyclic gas and water injection in a quasi-2D Hele-Shaw cell packed with soft hydrogel particles at varying initial porosities. High-resolution imaging and pressure monitoring are used to measure gas entry pressure (increasing with decreasing porosity, consistent with Young-Laplace), shifts in invasion regime (cavity-dominated at high porosity to pore invasion at low porosity), pressure-drop statistics, increasing residual gas saturation with cycle number (higher at low porosity), and power-law scaling of specific interfacial length with gas cluster size (exponent decreasing with lower porosity and more cycles). The central claim is that gas trapping depends on both initial packing structure and cyclically evolving gas-solid interactions.
Significance. If the reported trends are robust, the study supplies quantitative experimental links between porosity, cyclic history, invasion morphology, and trapping efficiency in a soft granular system. The direct correlation of pore-scale events with macroscopic pressure signals and the observation of parameter-free power-law interfacial scaling are strengths. These data could inform constitutive models for repeated gas injection in deformable media relevant to geophysical and biophysical applications, provided the quasi-2D geometry is appropriately qualified.
major comments (1)
- [Abstract] Abstract: The assertion that the experiments 'demonstrate that gas trapping in deformable porous media depends on both initial packing structure and cyclically evolving gas-solid interactions' rests on an untested assumption that the quasi-2D Hele-Shaw geometry and hydrogel mechanics capture the three-dimensional connectivity and deformation modes controlling trapping; no scaling argument or cross-dimensional comparison is supplied to show that the observed porosity and cycle dependencies survive the suppression of out-of-plane flow paths and particle rearrangements.
minor comments (3)
- [Abstract] Abstract: The sentence 'with scaling exponent decreases as porosity decreases and cycling progresses' is grammatically incomplete and should be rephrased for clarity.
- [Abstract] Abstract: Quantitative details such as the specific porosity values, number of injection cycles, measured power-law exponents, and any statistical variability (error bars or standard deviations) are omitted, which would strengthen assessment of the reported trends.
- The manuscript would benefit from an explicit limitations paragraph discussing how the quasi-2D confinement and hydrogel swelling mechanics may restrict direct extrapolation to natural three-dimensional deformable porous media.
Simulated Author's Rebuttal
We thank the referee for the positive evaluation and recommendation of minor revision. Below we address the single major comment point by point.
read point-by-point responses
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Referee: [Abstract] Abstract: The assertion that the experiments 'demonstrate that gas trapping in deformable porous media depends on both initial packing structure and cyclically evolving gas-solid interactions' rests on an untested assumption that the quasi-2D Hele-Shaw geometry and hydrogel mechanics capture the three-dimensional connectivity and deformation modes controlling trapping; no scaling argument or cross-dimensional comparison is supplied to show that the observed porosity and cycle dependencies survive the suppression of out-of-plane flow paths and particle rearrangements.
Authors: We acknowledge that the quasi-2D Hele-Shaw geometry inherently suppresses out-of-plane flow paths and full three-dimensional particle rearrangements, which is a genuine limitation of the experimental platform. The setup was selected to permit direct visualization and correlation of pore-scale invasion events with macroscopic pressure signals, features that remain challenging in opaque 3D packings. The reported porosity and cycle dependencies arise from local capillary entry (Young-Laplace) and contact-line pinning on deformable particles; these mechanisms are dimensionally local and therefore expected to persist qualitatively in 3D, although quantitative thresholds and cluster statistics may shift. No scaling argument or 3D comparison is supplied because the study is purely experimental and does not include theoretical modeling or additional 3D data. We will revise the abstract to read 'in a quasi-2D deformable porous medium' and add one sentence in the final section noting the geometric limitation and the need for future 3D validation. revision: partial
Circularity Check
No circularity: purely observational experimental study
full rationale
The paper reports direct experimental observations of gas invasion, pressure fluctuations, residual saturation, and interfacial length in a quasi-2D Hele-Shaw cell with hydrogel particles. No mathematical derivations, parameter fits presented as predictions, self-citation chains, or ansatzes are used to obtain the reported trends; all quantitative results (entry pressure scaling, regime transitions, pressure-drop statistics, saturation growth, power-law exponents) are obtained from imaging and pressure monitoring of the physical experiments themselves. The central claim follows from these measurements without reduction to quantities defined by the same data.
Axiom & Free-Parameter Ledger
Reference graph
Works this paper leans on
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[1]
https://doi.org/10.1007/s42452-019-1874-5 Merkus, H. G. (2009). Particle size measurements: fundamentals, practice, quality (V ol. 17). Springer Science & Business Media. Op Den Buijs, J., Lu, L., Jorgensen, S. M., Dragomir-Daescu, D., Yaszemski, M. J., & Ritman, E. L. (2009). Solute transport in cyclically deformed porous tissue scaffolds with controlled...
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[2]
http://dx.doi.org/10.1016/j.ijggc.2014.05.003. 30 Saeedi, A., & Rezaee, R. (2012). Effect of residual natural gas saturation on multiphase flow behavior during CO2 geo-sequestration in depleted natural gas reservoirs. Journal of Petroleum Science and Engineering, 82-83, 17-26. https://doi.org/10.1016/j.petrol.2011.12.012 Sandnes, B., Flekkøy, E. G., Knuds...
discussion (0)
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